1. Field of the Invention
The present invention relates to image forming apparatuses such as a copying machine and a printer.
2. Description of the Related Art
In image forming apparatuses such as a copying machine and a printer, an original stand on which an original is placed is exposed to light and reflected light from the original stand is guided to a photoelectric conversion element, for example, a CCD (charge coupled device). The CCD outputs an image signal corresponding to an image of the original. A laser beam corresponding to this image signal is irradiated on a photoconductive drum and an electrostatic latent image is formed on a peripheral surface of the photoconductive drum.
The electrostatic latent image formed on the peripheral surface of the photoconductive drum is visualized by a developing agent (a toner). A sheet is sent to the photoconductive drum to be timed to coincide with rotation of the photoconductive drum and a visible image (a developing agent image) on the photoconductive drum is transferred onto the sheet. The sheet having the developing agent image transferred thereon is sent to a fixing unit. The fixing unit includes a heating roller and a pressure roller that rotates together with the heating roller while being in contact with this heating roller in a pressing state. The fixing unit fixes the developing agent image on the sheet with heat of the heating roller while conveying the sheet with the sheet nipped between both the rollers. The heating roller incorporates an electric heater as a heat source.
On the other hand, to reduce waiting time of a user and for energy saving measures, it is desired to reduce time required for warming-up of the fixing unit.